11.09 Ovarian Function Flashcards
When does oogenesis start?
When does it finish?
Oogenesis begins in foetal life but it is arrested in the second meiosis. This gives rise to all the primary oocytes. These are arrested in the first meiotic division.
It reassumes division in puberty when menses begins.
It finishes when the finite number of oocytes run out in menopause
What are the two major reproductive hormones for females?
Oestrogen and Progesterone in females come from follicular cells and corpus luteum
What is menses?
When the endometrial lining of the uterus sloughs off and begins the classic menstrual cycle
Describe the menstrual cycle
- Begins at puberty
- Interrupted by pregnancy (because the endometrium is retained for the embryo)
- Terminated by menopause
- Length of 28 days – cyclic process
- It has two phases:
- Follicular phase (Proliferative endometrium)
- Luteal Phase (Secretory)
What is meant by the uterine cycle?
The same as the mentrual cycle but described in relation to the endometrium instead of the ova.
The uterine cycle:
- Proliferative phase where the endometrium builds up to support implantation dominated by oestrogen.
- Secretory phase dominated by both progesterone and oestrogen which secretes nutrients that are meant to support the implanted cell
What are the female secondary characteristics?
- Characteristics controlled by estrogen: Breast development and Distribution of body fat
- Adrenal androgens control some female traits like Growth of pubic and axillary hair and Sex drive (libido)
What are the labiam major and labiam minor
Skin folds protect the sensitive area. No ascending rising bacteria particularly during pregnancy - labium minora and labium majora. With the anus at a distance
What are the 2 major layers of the uterus?
The first (inner lining) of the uterus is the endometrium.
The myometrium is the muscle layer that contracts and delivers the baby from the uterus.
Both layers are highly vascularised
Describe the anatomy of the female reproductive system
The vagina ends in the cervix (which is normally long, thick and closed which dilates and apphase 10cm to allow delivery of the baby).
The cervix deliniates the vagina from the uterus which is connected by fallopian tubes to fimbraie (finger like structures).
The ovaries lie near the fimbrae - NOT PHYSICALLY ATTACHED to them. This means the egg is released in the vicinity of the fimbrae and they “pick it up”
Describe oogenesis occuring in the ovary in the context of anatomy
Maturation changes the oocyte to become mature and fluid filled for nutrition and that is what is ovulated.
Mature oocytes are ejected from the ovary (through a tearing in tissue). The follicle is left behind and differentiates into the corpus luteum (and eventually dies off if there is no firtilisation).
Describe the microanatomy of the a mature follicle
- Surface epithelium
- Thecal cell layer which responds to LH and are responsible for androgen release
- Basal lamina
- Granulosa cell layer which responds to FSH and turns the androgens into oestrogen as well as releasing inhibin for negative feedback purposes
- Antral fluid is important for nutrient supply
What is a polar body?
Either of the two small cells produced during the first and second meitoic divisions in the development of an ooxyte that contains little cytoplasm and eventually degrades.
The genome is equally divided between daughter cells in meiosis of oogenesis but not the cytoplasm,
Describe the three phases of the menstrual cycle (including timing)
- Follicular / Proliferative phase
- Follicle growth in ovary (egg matures)
- Endometrium builds up in preparation
- Days 0‐13
- Ovulation
- Ripened follicles and release of oocyte(s)
- Day 14
- Luteal / Secretory phase
- Ruptured follicle transforms into corpus luteum in preparation for pregnancy
- Days 15‐28
Describe the three phases of the endometrial lining (ie. the uterine cycle)
- Menses
- No pregnancy
- Bleeding from uterus as endometrium is shed
- Proliferative phase
- New layer of endometrium in preparation of pregnancy
- Secretory phase
- Conversion of endometrium to secretory structure to promote implantation
How does the basal body temperature of a woman change with ovulation?
Basal body temp of a woman changes very lightly during the menstrual cycle with an increase in temperature just AFTER the menstrual cycle. Useful in tracking ovulation
Describe the hormonal changes that occur during the follicular phase of the menstrual cycle
- The GnRH release causes a release of FSH and LH
- Together they stimulate and support follicular maturation: antral formation to the point 1 dominant follicle is present
- LH causes thecal cells to release androgens which negatively feeds back to LH production
- FSH acts on granulosa cells to convert the androgens into oestrogen (using aromatase enzyme)
- Oestrogen has a positive feedback loop to granulosa cells to make more oestrogen = increasing oestrogen levels
- Oestrogen has a negative feedback loop on FSH and LH keeping them at tonically low levels
This whole time, menses is occuring from the failed implanation from the previous cycle
Describe the hormonal changes that occur during the ovulatory phase of the menstrual cycle
- The rising oestrogen from the positive feedback reaches a THRESHOLD that changes the negative feedback on LSH and FSH into positive feedback
- LH and FSH surge
- Oestrogen also causes the cervical mucous to become thinner (in preparation for the sperm to be able to swim through)
- Oestrogen supports proliferation of the endometrium and expression of progesterone receptors in perparation
- This surge triggers ovulation to occur
- Granulosa cells of the released oocyte release inhibin which quickly brings and keeps FSH and LH levels down to prevent another follicle maturing
- Also releases some progesterone
- The follicle that remains differentiates into the corpus luteum and oestrogen levels begin to fall
Describe the hormonal changes that occur during the luteal phase of the menstrual cycle
- The differentiated follicle is now the corpus luteum. This means there is no more source for oestrogen
- Increase in basal body temperature
- Cervical mucous becomes thick
- The mature corpus luteum becomes steroidogenic and releases high amounts of progesterone
- Progesterone receptors on the endometrium enable it to be maintained
- Some oestrogen is also released to maintain the endometrium
- Corpus luteum also secretes high levels of inhibin to prevent FSH and LH levels increasing
Pregnancy = maintained state
No Pregnancy = Corpus luteum dies leaving no source for progesterone and oestrogen leading to endometrial sloughing and a removal of the negative inhibtion on FSH and LH such that the cycle can start again.
What is the acrosome reaction?
The acrosome is the cap structure of the sperm head.
The acrosome reaction occurs when the sperm approaches the zona pallucida around the ova. The acrosome fuses with the plasma membrane of the oocyte and exposes contents like surface antigens and digestive enzymes that break through the egg’s coating to allow fertilisation.
Describe what happens to the zygote once fertilisation occurs
Fertilisation leads to a zygote which undergoes multiple cell divisions forming the morula (ball of cells). When this enters the uterus (day 4/5) it becomes the blastocyst with an inner cell mass (to become the foetus) and the trophoblast cell (placenta)
Around day 5-9 there is implantation (this can only happen if the endometrium is appropriately nourished). It gets buried completely in the endometrium because it needs the nutrients, oxygen and blood flow to grow and develop. Many don’t get to this point - 30-50% of successful fertilisations don’t get to this point.
Describe the embryonic period (3-8 weeks) of pregnancy and the dangers faced here
- Most susceptible to teratogens
- All major organ systems present
Describe the foetal period of pregnancy and the dangers present to the foetus at this stage
The foetus (defined as a foetus from 9 weeks onward)
- Rapid growth
- Physiological defects
- Minor morphological abnormalities (as organs already developed)
- Functional disturbances
